The “Fat Leonard” corruption investigation has expanded to include more than 60 admirals and hundreds of other US navy officers under scrutiny for their contacts with a defence contractor in Asia who systematically bribed sailors with sex, alcohol and other temptations, according to the navy.

Most of the admirals are suspected of attending extravagant feasts at Asia’s best restaurants paid for by Leonard Glenn Francis, a Singapore-based maritime tycoon who made an illicit fortune supplying navy vessels in ports from Vladivostok, Russia, to Brisbane, Australia. Francis also was renowned for hosting boozy after-dinner parties, which often featured imported prostitutes and sometimes lasted for days, according to federal court records.

The 158kg Francis, also known in navy circles as “Leonard the Legend” for his wild-side lifestyle, spent decades cultivating relationships with officers, many of whom developed a blind spot to his fraudulent ways.

The Justice Department has filed criminal charges against 28 people, including two admirals, since Francis was arrested in an international sting operation four years ago. Those cases form the worst corruption scandal in navy history, but they represent a fraction of a much larger list of navy officials under investigation but whose names have mostly been kept secret.

In response to queries from The Washington Post, the navy confirmed that it has been reviewing the conduct of 440 other active-duty and retired personnel – including 60 current and former admirals – for possible violations of military law or federal ethics rules in their dealings with Francis and his company, Glenn Defence Marine Asia.

That is double the number of admirals whom navy officials said were under investigation last year. The US navy has about 210 admirals on active duty.

The caseload has grown as the Justice Department has given the navy additional dossiers of individuals who did not meet the threshold for prosecution in civilian courts, but may have committed offences under the military justice system, officials said.

So far, the navy has charged five people with crimes – none of them admirals – under military law, charging documents show.

In addition, the navy said 40 people committed misconduct by violating ethics rules or other regulations. Their cases have been handled administratively, meaning they did not involve criminal charges.

Francis, 53, is in jail in San Diego as he awaits sentencing in federal court. He pleaded guilty in 2015 to bribing “scores” of navy officials and defrauding the service of more than US$35 million.

His widespread overbilling of the navy had been an open secret for years. In response to a flood of fraud complaints, the Naval Criminal Investigative Service (NCIS) opened more than two-dozen separate investigations into Glenn Defence, according to law-enforcement records.

Most of the cases went nowhere, NCIS files show. Starting in 2009, however, NCIS escalated its efforts by assigning more agents to investigate Francis. It later opened a full-blown corruption inquiry on suspicion that some navy officials were feeding him military secrets and inside information about defence contracts.

Despite being under the microscope, Francis was still able to rub shoulders with many of the Navy’s top leaders.

In September 2011, for example, he was invited to the Naval Academy in Annapolis to attend a change-of-command ceremony for the navy’s highest-ranking officer.

During his visit, Francis posed for grip-and-grin photos with Admiral Jonathan Greenert, the new chief of naval operations, and the man he was replacing, Admiral Gary Roughead.

Roughead and Greenert met Francis during prior assignments in Asia and the Pacific. A navy spokesman would not say whether they are among the 60 admirals under investigation.

Roughead said in an email that he could not “recall particulars” about who was invited to the event and declined to comment further.

In an email, Greenert said he had not been contacted by investigators and did not know who invited Francis to the ceremony. He said he, Roughead and their spouses spent hours in a receiving line and posed for several pictures.

Of the two admirals, Greenert’s previous contacts with Francis were more extensive, according to several sources.

Greenert met the defence contractor in the late 1990s while serving as chief of staff for the navy’s 7th Fleet, which covers most of Asia. Their interactions continued after Greenert was promoted to vice admiral and took command of the fleet in 2003.

While in command, Greenert attended at least three dinners with Francis, according to two former senior navy officials.

In December 2005, Greenert sent Francis a Christmas card with a sketch of the USS Blue Ridge, the 7th Fleet flagship, which the contractor had often visited as a distinguished guest.

“Leonard – See you soon I expect. Recognise the ship?” Greenert joked in a handwritten note wishing him “Good health & happiness in 2006.”

Three months later, Greenert signed a letter on official stationery thanking Francis for the “superb services” his company provided to the Blue Ridge during several port visits in southeast Asia. “Over the years, the reputation of Glenn Marine remains exceptional,” the letter stated. “Keep up the great work.”

Francis treasured such letters, cards and photographs, which he promoted as proof of his close ties with senior navy leaders. Greenert posed for photographs with Francis on at least two other occasions: on board the Blue Ridge in 2005 and at a ceremony in Hawaii in 2009.

Greenert insisted it was not unusual for commanders to send correspondence to contractors acknowledging their “responsive and flexible” service. He also said he sent hundreds of official Christmas cards during his time as the 7th Fleet commander. He did not respond to questions about dinners he attended with Francis or other interactions.

Greenert’s relationship with Francis later became a sensitive issue for NCIS agents.

As the law-enforcement inquiries into Francis and his company heated up in 2013, NCIS officials deliberately kept Greenert, who by then was chief of naval operations, in the dark, according to two former senior navy officials.

Even after Francis was arrested, NCIS officials excluded Greenert from briefings about the case, restricting their reports to a handful of navy civilian leaders and Admiral Mark Ferguson, who was then the vice-chief of naval operations, according to the former senior officials.

In addition to Roughead and Greenert, Francis secured photo-ops with several other high-ranking admirals during his visit to the Naval Academy in 2011.

He also spent time in Annapolis with Vice-Admiral Michael Miller, the academy superintendent at the time, who arranged for a personal tour of his official residence, Buchanan House, according to photographs obtained by The Washington Post.

In a statement, Miller confirmed the meeting but said he had “no knowledge” that Francis was under investigation at the time.

The navy later rebuked Miller for failing to adequately reimburse Francis for lavish dinners and other gifts he received from the contractor years earlier when he commanded an aircraft carrier strike group in Asia.